Set up LTM module and then Configuring a Sync-Failover device order of configuration

Here the order of configuration does not matter. You can create VS or any objects on F5-A even before configuring a Sync-failover device group. All it requires is the module to be present. Make sure the license applies to this module too.

On the other hand, you can provision LTM modules on both F5-A & F5-B and then go configure device group. Then go with creating the setup in F5-A.

Hint: Network configuration(device level) is different than application configuration (Object level), So either way, you would achieve the results.

Creating a Sync-Failover device group